22nd International Symposium on Plasma Chemistry
July 5-10, 2015; Antwerp, Belgium
Time-resolved in situ UV absorption spectroscopic studies for detection of
reactive oxygen and nitrogen species (RONS) in plasma activated water
J.-S. Oh1,2, S. Ito1, H. Furuta1,2 and A. Hatta1,2
1
Department of Electric and Photonic Systems Engineering, Kochi University of Technology, 185 Miyanokuchi,
Tosayamada, Kami, 782-8502 Kochi, Japan
2
Center for Nanotechnology, Research Institute of KUT, 185 Miyanokuchi, Tosayamada, Kami, 782-8502 Kochi, Japan
Abstract: Plasma activated water (PAW) is receiving a lot of attention in biomedical
applications since its high bactericidal properties. In this work, we used a conventional
UV-VIS spectrometer associated with a custom-built-sample chamber which enables in-situ
measurement. UV absorption according to reactive oxygen and nitrogen species (RONS)
in PAW generated was successfully measured during an atmospheric-pressure helium
plasma jet irradiation.
Keywords: in-situ UV absorption, plasma activated water, plasma jet, reactive species
1. Introduction
Plasma activated water (PAW) also referred to as
plasma treated water (PTW) are rapidly gaining
importance in biomedical applications, particularly for the
inactivation of microorganisms [1-3]. Atmosphericpressure plasma jets (APPJs) are a candidate to induce
reactive oxygen and nitrogen species (RONS) in water.
APPJ is well-known that can generate various reactive
species by an interaction between emerging plasma and
ambient air, and its gas flow can deliver the generated
species on a target surface.
Many RONS in PAW are open discussed e.g. hydroxyl
radical (OH•), nitric oxide radical (NO•), singlet oxygen
(1O 2 ), ozone (O 3 ), superoxide anion radical (O 2 −•),
hydroperoxyl radical (HOO•), nitric dioxide radical
(N 2 O•), hydrogen peroxide (H 2 O 2 ), nitrate (NO 3 −) and
nitrite (NO 2 −). For the detection of the plasma-generated
RONS in liquid solution, electron spin resonance (ESR)
[4], ion chromatography [2], free radical scavenging
[2, 5], Fourier transform infrared spectroscopy (FTIR) [6]
and UV-VIS absorption spectroscopy [6, 7] are often
used.
A similar work of PAW using helium APPJ has been
reported by Ikawa et al. [2] who observed O 2 −•, HOO•,
H 2 O 2 and NO x − in the PAW. Among them O 2 −• and
HOO• have short half-life (< several seconds) and H 2 O 2
and/or NO x − have relatively long lifetimes (< min). In
our report, we measured UV absorption according to
RONS in PAW mentioned above and investigated the
temporal behaviour.
2. Experimental procedure
An APPJ generated by a cylindrical dielectric barrier
discharge (DBD) system was used in this work. The
plasma jet apparatus consisted of a 150 mm long glass
tube with a 2.4 mm inner diameter. Helium gas was fed
into the glass tube with a fixed gas flow rate of 2 slm
through a digital flowmeter. High-voltage bipolar square
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pulse of 7 kV (peak-to-peak) at a frequency of 10 kHz
was applied to a metallic external electrode.
A commercially available double-beam UV-VIS-NIR
spectrometer (Hitachi, U-3900) and a custom-builtsample chamber were used. These enable to measure the
optical property of the PAW temporally and in situ. The
spectrometer used in this study could detect to down to a
wavelength of 190 nm with fixed spectral resolution of
0.2 nm and scan speed of 120 nm/min. An optical path of
the light is fixed distance of 10 mm. A 600 µm thick
quartz plate (VIOSIL-SX, Shinetsu Chem. Ltd.) was used
as a barrier of the gas flow. The quartz has a high
transmittance over 90% in the broadband wavelength
between 190 and 900 nm (Fig. 1).
High voltage
(10 kHz, 7kV )
Glass tube
Ring electrode
APPJ
10 (mm)
Teflon housing
30 (mm)
15 (mm)
IR
IS
Empty cuvette
(reference)
U-3900 spectrometer
IS
PAW
I
(I0: untreated)
(sample)
Fig. 1. In-situ UV absorption spectroscopy for detection
of reactive oxygen and nitrogen species (RONS) in
plasma activated water.
1
3. Results and discussion
The transmitted spectra of untreated DI water I 0 and
PAW I were measured between 190 and 340 nm. The
transmitted spectra were converted into absorbance (Abs)
using an equation (1) below,
𝐴𝐴𝐴 = −𝑙𝑙𝑙 �𝐼�𝐼 �.
(1)
0
The transmittance of PAW decreased across a specific
UV range between 190 nm and 250 nm; no other intensity
changes in the visible and near-infrared range between
400 and 900 nm were measured.
Fig. 2a shows a schematic of plasma jet irradiation for
DI water (4 mL). Transmittance is decreased as a
function of time as shown in Fig. 2b. Using eq. (1)
transmittance was converted into absorbance, we
observed absorption spectra having a broad width of
~30 nm and the peak at around 206 nm. A close
inspection of Fig. 2c shows there is a peak shift: the
absorption peak wavelength became shorter from
207.4 nm to 205.8 nm as function of time and eventually,
it became stable at the peak wavelength of 205.8 nm after
20 min exposure to the plasma jet irradiation. The
absorbance is also increased as function of time. It should
note that the negative absorbance of the case of the direct
APPJ exposure (10 min) at short wavelength range below
200 nm was caused by helium gas flow reduced O 2 (aq.)
concentration in the liquid [8].
Transmittance (%)
15 mm
100
10 min
20 min
30 min
90
80
70
I
IS
200
240
280
320
Wavelength (nm)
(a)
Absorbance [-log(I/I0)]
0.1
110
30 min
20 min
10 min
0.08
0.06
0.04
0.02
0
200
240
280
320
Wavelength (nm)
(b)
(c)
Fig. 2. (a) schematic of in-situ measurement of absorption spectra of DI water by a direct irradiation of APPJ, (b)
transmittance of PAW as function of time and (c) converted absorbance from the transmittance.
2
0.5 209.2 nm
0.4
0.3
0.2
0.1
0
201.4 nm
1.5
1
NaNO2 (6.62 ppm)
HNO3 (6.45 ppm)
0.5
Absorbance
Here we discuss the chemical composition of the PAW.
As mentioned above, it is open reported that the longliving RONS typically H 2 O 2 and NO x are in PAW.
However there is no report of UV absorption
spectroscopy at the short wavelength range. Thus we
measured the absorption spectra for diluted H 2 O 2 , HNO 3 ,
and NaNO 2 , respectively, with several different
concentrations. Typical absorption spectra of the three
reference solutions are shown in Fig. 3. We see the both
NaNO 2 and HNO 3 have a broad width and absorption
peaks between 200 and 210 nm, while H 2 O 2 has no peak
in the region. The both absorption profiles of NaNO 2 and
HNO 3 are very similar to the absorbance spectrum of
PAW in Fig. 2c. However NO x cannot clearly explain the
absorption tail at longer wavelength over 250 nm, H 2 O 2
should be included in PAW. From the measurement of
reference solutions, it is believed that the most RONS
generated in the plasma-air interaction and transported by
the gas flow [9].
Fig. 4a shows a simple experiment with a quartz barrier
which placed on the top of DI water filled in the cuvette
to block the gas flow but to transmit UV photons mainly
related 2nd Positive N 2 . Figs. 4b for the transmittance and
4c for absorbance show no significant absorption. The
result indicated high energy UV photons play a minor role
to generate reactive species in PAW. We also confirmed
that there are no significant effect of UV photons using
three standard D 2 , Xe arc, and mercury lamps.
0
0.8
H2O2 (6.25 ppm)
0.6
0.4
250 nm
0.2
0
200 220 240 260 280 300 320 340
Wavelength (nm)
Fig. 3. Absorbance spectra of reference solutions (a)
NaNO 2 (6.62 ppm), (b) HNO 3 (6.45 ppm), and (c) H 2 O 2
(6.25 ppm) diluted in DI water, respectively.
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22nd International Symposium on Plasma Chemistry
July 5-10, 2015; Antwerp, Belgium
Transmittance (%)
110
Quartz
100
10 min
20 min
30 min
90
80
70
I
IS
200
240
280
320
Wavelength (nm)
(a)
(b)
Absorbance [-log(I/I0)]
0.1
30 min
20 min
10 min
0.08
0.06
0.04
0.02
0
200
240
280
320
Wavelength (nm)
(c)
Fig. 4. (a) schematic of in-situ measurement of absorption spectra of DI water by an irradiation of APPJ onto a quartz
plate, (b) transmittance of DI water as function of time and (c) converted absorbance from the transmittance.
[9]
4. Conclusions
Using an in-situ absorption spectroscopy we
successfully measured UV absorption of PAW induced by
an APPJ irradiation. The absorption spectrum has a
simple spectral profile indicated its simple chemical
composition of NO x and H 2 O 2 . Using a quartz barrier it
remarked the RONS were generated by emerging plasmaambient air interaction and the He gas flow played a very
important role in the transportation of plasma-generated
RONS into DI water.
J.-S. Oh, et al. J. Phys. D: Appl. Phys., 44, 155206
(2011)
5. Acknowledgements
This work was supported by the Priority Research
Grant of KUT and partly by MEXT KAKENHI Grant-inAid for Challenging Exploratory Research (Grant number
26600129). We wishes to thank Dr. Petr Lukeš at the
Institute of Plasma Physics, Academy of Sciences of the
Czech Republic and also Prof. Katsuhisa Kitano at
Graduate School of Engineering, Osaka University for the
valuable comments on the UV absorption spectra.
6. References
[1] P. Bruggeman and C. Leys. J. Phys. D: Appl. Phys.,
42, 053001 (2009)
[2] S. Ikawa, et al. Plasma Process. Polymers, 7, 33-42
(2010)
[3] P. Lukeš, et al. Plasma Sources Sci. Technol., 23,
015019 (2014)
[4] A. Tani, et al. Appl. Phys. Lett., 100, 254103 (2012)
[5] E. Takai, et al. Plasma Process. Polymers, 9, 77-82
(2012)
[6] K. Oehmigen, et al. Plasma Process. Polymers, 8,
904-913 (2011)
[7] K. Sakuramoto, et al. in: Abstracts of 5th ICPM.
166 (2014)
[8] J.-S. Oh, et al. Biointerphases, submitted (2015)
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